Centering arrangement and method for beams of cathode ray tubes



A. D. GIACCHETTI 2,915,662

CENTERING ARRANGEMENT AND METHOD FOR BEAMS OF CATHODE RAY TUBES De c. 1, 1959 INVENTOR.

xw J477'0ENE Y- Filed Aug. 24, 1956 F1" 5. i. 2*?- i2 United States Patent "ice Anacleto D. Giacchetti, Chicago, Ill., assignor to National Video Corporation, Chicago, Ill.

Application August 24, 1956, Serial No. 606,010

3 Claims. (Cl. 313-76) This invention relates to cathode ray tubes and more particularly to a means and method for aligning the electron beam thereof with apertures in the gun structure.

The invention is intended to be applied in connection with what are described in this art as straight guns and which do not include means for trapping negative ions, as contrasted with guns of the type which are pro- .vided with a slashed anode or a bent anode cooperative with magnetic means exteriorly of the tube neck for trapping the negative ions to prevent them from reaching the luminescent screen. A large proportion of present-day television picture tubes include a screen of the usual phosphors carried in a binder upon the rear face of which aluminum is vaporized to provide a practically monomolecular metallic lamina which will allow suitable activation for electroluminescencebut will effectively intercept the negative ions to avoid screen burn.

. Notwithstanding the most rigid manufacturing techniques it frequently happens that true axial alignment of the apertures of the several electrodes of the straight electron gun of a cathode ray tube is not achieved.

The result of such misalignment, when of the minor character with which the present invention is concerned, is to cut off some portion of the beam whereby the scanning spot on the screen assumes a non-circular configuration. Since, ideally, a properly aligned and focused beam shall be a true circle at the point of impingement on the screen any departure therefrom can result in rejection by 'the purchaser. The non-circularity here noted may take various forms, e.g. ovoid, a circle having a localized circumferential protuberance or nodule thereon or similarly distorted non-circular forms.

This invention has for its principal object the provision of magnetic means internally of the tube whereby appropriate correction may be applied to the principal direction of the beam and the same caused to assume a position at which interference thereof with the margin .ofone or more apertures of the gun is anacceptable minimum consistent with the focusing, scanning and accelerating forces to which the beam is ordinarily also subjected. I g I A further object is to provide beam-correcting means which, notwithstanding its location within the tube neck, may be adjusted without the necessity of destroying the tube.

Another object is to provide beam-correcting means capable of'being employed in vectorial fashion in order that the direction and magnitude of the applied correcting. force applied to the beam may be chosen at will.

An additional object resides in a method of beam correction.

Other dbjects and advantages will become apparent from the following description which, taken together with the accompanying drawing illustrates certain forms which the invention may assume in practice.

In this drawing: Fig. 1 shows the neck and base portions of ray tube incorporating the invention;

a cathode I 2,915,662 Patented Dec. 1, 1959 Fig. 2 is a cross section taken on the line 2-2 and showing the magnetizing device in use; and

Figs. 3 to 9 illustrate various modes of arranging the internal centering means.

Regarded in a broad sense the invention comprehends the provision of a plurality of permanent magnets permanently secured to an electrode of the electron gun, preferably in a region of low acceleration of the beam e.g. the screen grid or upon a support other than an electrode. A plurality of magnets is employed, e.g. three in number, distributed equi-angularly about the beam axis and preferably aligned in a plane transverse thereto. The magnets may be magnetized in a selected grouping and with a selected intensity of magnetization to provide a magnetic field having a magnitude and direction of a character to deflect the beam with a force and a direction to align the same with the apertures of the. several electrodes to the greatest possible extent consistent with the other forces to which the beam is subjected. Magnetization and de-magnetization of the magnets is accomplished by well-known instrumentalities' applied exteriorly of the tube, e.g. a coil and a yoke therefor arranged to be brought into adjacency with the magnets and energized by DC or A.C. as the case may be. Thus, after initially determining the direction of mis-centering by visual inspection of the spot on the screen the required. correction may be applied to conform the spot as nearlyas possible to a true circle. Turning to the drawing I have shown the neck 10 o a cathode ray tube 11 which includes an electron gun assembly 12 of the electrostatic focusing type. In order to simplify the drawing no supports are shown for the several electrodes. However, it will be understood that the supports maintaining the position of the several electrodes relatively to each other and to the neck 10 are well known and may take any convenient form, eg glass cane into which radial support arms of the electrodes are fused while the same are fixed in a suitable l Desirably the plurality of permanent magnets comprising the internally mounted beam centering means of the invention are mounted about the internal periphery of the screen grid electrodelS. For example, in Fig. 2 I haveshown three such magnets 16a, 16b and of suitable magnetizable material and high retentivity for small volume, e.g. Alnico V.

Before adverting to details of mounting the magnets and the form, they may take the basic centering operation will be described in connection with Fig. 2. The

aperture in the screen grid 15 is indicated at 21 and it will be understood that the electron beam B from the cathode 20 (Fig. 1) has its path therethrough. Assuming such relative mispositioning of the aperture 15 and beam B as will cut off a portion of the beam and result in the aberration of the spot heretofore alluded to, the

invention comprehends the establishment of a permanent facturing technique the correction, both as to amount and direction, can be visually determined by viewingthe distorted spot on the screen while the tube is mounted on a test rack and providing correction in a mannerto produce as nearly perfect circularity as possible. It Will be seen that, by utilizing a plurality of magnets, such as 16a, and magnetizing them selectively, either singly or in pairs, with a predetermined flux, a resultant vector Y or. a reasonably practicalequivalent thereof can be produced. For example, assuming that X is at an angle of 210 (Fig. 2) then magnets 16a and 16b positioned at 90 and 330 respectively may be magnetized to provide, jointly, a force vector Y at 30. The intensity of mag netization imparted to magnets 16a and 16b can be easily controlled and will be selected to yield the correct magnitude of vector Y.

The magnetizing force is applied from an external device comprising a winding 24 wound on when yoke 25 having pole faces 26-26 conformed to the exterior diameter of the neck and an angular relation corresponding to the position of the magnets 16a, etc. Accordingly,

if the magnets 16a and 16b are to be influenced the parts will be in the position'of Fig. 2. Direct current of the .necessary polarity and voltage will be applied over the conductors 27-27 from a source 28. Regulation is. eifected'through a'rheostat 29. A polarity reversing switch may be introduced at theterminals 28. It will be understood that one polarity appliedto winding 24 will produce a magnetic field in one direction through the magnets, such as 16a, while reversal thereof is simply the result of reversing the applied polarity. Should error be made either in the direction and/ or magnitude of the correction the affected magnets may be de-magnetized by application to the leads 27, through a suitable switch, of AC. and the procedure then repeated.

The magnets, such as 160, may be mounted in any convenient manner and desirably with a. ferromagnetic connecting yoke. For example, Fig. 3 illustrates the Y magnets 16 secured in apertures provided in an annular iron yoke 31 which assembly may be secured to the screen gridby force-fitting the same therewithin, or by fastening elements.

Fig. 4 shows another mounting in'which more rigid 4 p sincespace in that region of the tube is at a premium, being provided with one or more deflection coils and focusing coils, such prior art devices havenot met with Moreover, the trend morerecently has been favor. toward shortening the tube neck in order to reduce the front to back dimension of the assembled receiver.

It will be understood that, while a separate ferromagnetic yoke for the permanent magnets is shown, it is within contemplation to provide-a'one-piece magnet having discrete pole'pieces disposed for establishment of a fiux field of the required magnitude and direction.

The term ferro-magnetic" is used herein to'designate materials, such as soft iron, having a high magnetic permeability in relation to air but no undue remanence.

The invention is also applicable to tubes wherein a magnetic field is employed forfocusing. the centering means of the invention is desirably located prior to the focusing field so that the beam centering correction isapplied first. Furthermore the invention finds application to tubes provided with so-called ion trap magnets although, in general, I have found the need therefor does not arise as frequently in this type of'tube.

From the foregoing it will have become clear that lowed, in'the'direction of propagation of "the beam, by

an axially-apertured electrode surrounded the beam v whose primary function is to accelerate the beam and wherein an asymmetrical field due to said electrodes tends to deflect the beam from a predetermined direction,

radial positioning isassured by means of cars 32 overlying the inner faces of the magnets.

In Fig. 5 four magnets are shown, and are integrated With the yoke by riveting or other suitable method. The assembly may be mounted within or just beyond one or the outer end of the screen grid depending upon the space available.

Figs. 6 and 7 illustrate an arrangement in which four cylindrical magnets are frictionally held in pockets formed by displacing portions of a ferromagnetic disc 41 into semi-circular, opposed strap-like portions 42 through which the magnets are forced and thereby held. The disc 41 may be supported on the usual glass cane 4343 upon which other elements of the gun are carried in order to maintain a precise relationship between themagnets and the electrodes. Fig. 7 does not purport to show any details of the mounting since the same per se form no part of the present invention.

Fig. 8 shows an arrangement of three magnets held by complementary semi-circular deformations '51 in a pair of juxtaposed annular yoke parts 52 of ferromagnetic material. These latter may be riveted, spot welded or otherwise assembled. Spring clips 53 secured to the yoke retain the assembly radially in its relation to the electron gun. If desired the clips may be jointed to the framework of the gun or the electrodes to maintain axial position thereof.

The permanent magnet assembly may be of the type having a plurality of spaced magnetic bars forming a generally-segmented cylinder, such as is shown in Fig. 9,

wherein magnets 61 are alternated with yoke portions 62.

.art it has been :proposed to mount spot correcting magnets of adjustable character on the .outsideof the neck but means for returning the beam to said predetermined direction comprising: a plurality of permanent magnets greater than two positioned within the neck of the tube intermediate the first mentioned electrode and second mentioned electrode, said magnets being equally spaced about the axis of the aperture closely adjacent the beam but in non-obstructive relation therewith, said magnets being selectively magnetized with a polarity and intensity to provide jointly a resultant vector acting on the beam with a displacing force of principal direction substantially directly opposed to the direction of deflection of the beam from its true path and of magnitude to return the beam to its true path.

2. The combination in accordance with claim 1 wherein the screen grid electrode is a hollow cylinder and the plurality of magnets is mounted therewithin.

3. The combination in accordance with claim 1 Wherein the magnets are arranged in an annular array sepabeing constituted as a single annulus.

References Cited in the file of this patent UNITED STATES PATENTS 2,157,182 Malolf May 9, 1939 2,435,475 Stromeyer Feb. 3, 1948 2,456,474 Wainwright Dec. 14, 1948 2,580,675 Grivet et al. Jan. 1, 1952 2,597,383 Samuel May 20, 1952 2,609,516 Flory Sept. 2, 1952 2,619,607 Steers Nov. 25 1952 2,634,381 Kafka Apr. 7, 1953 2,640,868 Ingle June 2, 1953 2,681,421 Gethmann June 15 1954 2,717,323 Clay Sept. -6, 1955 2,795,717 Finkelstein et al. June 11, 1957 2,859,364 Bethold "2-....- Nov. 4, 195.8

In such cases 

